The internal combustion engine and its principles of operation are of course well-known. It is also known to produce a portable tool with a small internal combustion engine. Such a tool, for fixing fasteners to a workpiece, is disclosed in EP 0 316 468, U.S. Pat. No. 4,483,474 and U.S. Pat. No. 4,522,162.
EP 0 316 468 describes in detail the construction and operation of a fastener tool equipped with a combustion chamber, into which is introduced a fuel/air mixture, combustion of which (ignited by a spark) drives a piston/working member assembly. However this arrangement is such that the power output tends to vary from one combustive cycle to the next, within quite wide limits. This deficiency is not a serious problem for power tools of the type disclosed in the prior art, since the device can be designed such that the likely minimum power output of any single combustive event is above the maximum required to perform the desired activity (e.g. driving fasteners into a workpiece) with any excess kinetic energy being absorbed by the rigid surface of the workpiece. However, in other applications, such a solution is not feasible or desirable.